Halogen-Metal Interconversion with Dibromobithienyls.

Abstract

Anhyd. CuCl2 (74 g.) added at -70° to a soln. of 4-bromo-3-thienyllithium (from 570 ml. 0.92N BuLi and 107 g. 3,4-dibromothiophene), and the mixt. after 2 hrs. at -70° held overnight at room temp. and then cooled and treated with HCl gave 52% 4,4'-dibromo-3,3'-bithienyl (I), m. 129° (ligroine). 3,3'-Dibromo-2,2'-bithienyl (II) was similarly prepd. in 61% yield from 138 g. 2,3-dibromothiophene in 100 ml. Et2O, 630 ml. N BuLi, and 100 g. anhyd. CuCl2. The nuclear magnetic resonance (n.m.r.) spectra of the products showed no rearrangement had occurred during the coupling. A soln. of 16.2 g. I in 100 ml. dry tetrahydrofuran added over 5 min. to 130 ml. 1.2N BuLl at -70°, the mixt. after a few min. poured onto solid CO2, and the reaction mixt. hydrolyzed gave 80% 4,4'-dicar- boxy-3,3'-bithienyl, prisms, decompd. 275-80° (HOAc) (n.m.r spectrum detd.); di-Me ester (by reaction with CH2N2) m. 147-8°. 3,3'-Dicarboxy-2,2'bithienyl, decompd. 289-91° [Owen and Nord (CA 46, 9554a) previously gave the m.p. as 175-85°], was prepd. in 70% yield from 10 g. II and 76 ml. 0.92N BuLi. [on SciFinder(R)]